Loans Receivable and Allowance for Loan Losses (Details 2) (USD $)	12 Months Ended			3 Months Ended	6 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Jun. 30, 2014	Sep. 12, 2014	Jul. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	$ 29,589,000	$ 37,040,000	$ 61,217,000
Provision for loan losses (credited) charged to operations	(9,469,000)	19,601,000	40,400,000
Accrued interest receivable	36,628,000	37,926,000
Loans (gross) amount	11,909,722,000	12,386,378,000
Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortizing hybrid ARM fixed rate period one	5 years	3 years
Amortizing hybrid ARM fixed rate period two	7 years
Amortizing hybrid ARM fixed rate period three	10 years
Amortizing interest-only hybrid ARM fixed rate period two, prior to the 2010 fourth quarter	5 years
Amortizing interest-only hybrid ARM fixed rate period three, prior to the 2010 fourth quarter	7 years
Interest-Only Hybrid ARM Loans, Interest-Only Payment Term	10 years
Residential mortgage loans | Geographic concentration risk | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total	5.00%
Non-performing multi family mortgage loans | Multi family and commercial real estate mortgage loan | New York Metropolitan Area [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total	85.00%
Non-performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans, interest that would have been recognized	5,600,000	15,600,000	16,800,000
Actual payment recorded as interest income	3,600,000	6,200,000	4,300,000
Total loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	29,900,000	31,700,000
Mortgage loans (gross)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (gross) amount	11,660,354,000	12,146,697,000
Mortgage loans (gross) | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	19,868,000	26,644,000	49,794,000
Provision for loan losses (credited) charged to operations	(23,464,000)	9,368,000	24,663,000
Loans (gross) amount	6,873,536,000	8,037,276,000
Mortgage loans (gross) | Residential mortgage loans | Pre 2007 interest only loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (gross) amount	1,060,000,000	1,660,000,000
Mortgage loans (gross) | Residential mortgage loans | Reduced documentation loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (gross) amount	1,020,000,000	1,240,000,000
Mortgage loans (gross) | Residential mortgage loans | Reduced documentation loans | SISA (stated income, stated asset) loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (gross) amount	148,900,000	193,000,000
Non-performing loans held-for-sale, net | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs					8,700,000
Non performing residential mortgage loans transferred to held for sale					195,000,000
Non performing residential mortgage loans held for sale					186,300,000
Provision for loan losses (credited) charged to operations					(5,700,000)
Carrying value, loans sold						4,000,000	173,700,000
Gain (loss) on sales of loans, net				$ 920,000